'Bus-ing stands' allow passengers to reach aircraft that are parked on 'remote' gates.
Not all stands have passenger jetties or air-bridges that connect to the terminal buildings.
Some stands are 'remote' because it allows for extra rows of parking spaces, without having to build additional terminal buildings, for example gates 524 to 527 which don't connect to terminal 'A'.
Also, jetties aren't long enough to reach the furthest stands 531 & 541 on terminal 'B'. And the same goes for stands 551, 558, 567 & 568 on terminal 'C'. (Although 561 does have a jetty, and it always seems like it might be the longest jetty in the world!!)
There is also an 'imaginary' terminal 'D' at Heathrow that hasn't been built, next to the fire station. Terminal 'D' allows for stands numbering in the 570's, 580's and 590's. All of these require a bus to reach them.
Finally, stands 504 and 510 are 'missing'. There are a few reasons I can think of for this:
- They can be used to get passengers onto buses.
- They allow stands 505, 508 & 512 to be larger, to park larger aircraft.
- They allow stands 505 & 512 to be 'Muster' stands, so that passengers can be directed there safely in case of a terminal fire/evacuation.